lwsac_use_zeroed: lwsac helper equivalent to zalloc

include/libwebsockets/lws-lwsac.h

@@ -99,6 +99,24 @@ lws_list_ptr_insert(lws_list_ptr *phead, lws_list_ptr *add,
 LWS_VISIBLE LWS_EXTERN void *
 lwsac_use(struct lwsac **head, size_t ensure, size_t chunk_size);
 
+/**
+ * lwsac_use - allocate / use some memory from a lwsac
+ *
+ * \param head: pointer to the lwsac list object
+ * \param ensure: the number of bytes we want to use, which must be zeroed
+ * \param chunk_size: 0, or the size of the chunk to (over)allocate if
+ *			what we want won't fit in the current tail chunk.  If
+ *			0, the default value of 4000 is used. If ensure is
+ *			larger, it is used instead.
+ *
+ * Same as lwsac_use(), but \p ensure bytes of memory at the return address
+ * are zero'd before returning.
+ *
+ * Returns NULL if OOM.
+ */
+void *
+lwsac_use_zeroed(struct lwsac **head, size_t ensure, size_t chunk_size);
+
 /**
  * lwsac_free - deallocate all chunks in the lwsac and set head NULL
  *

lib/misc/lwsac/lwsac.c

@@ -131,6 +131,17 @@ lwsac_use(struct lwsac **head, size_t ensure, size_t chunk_size)
 	return (char *)(*head)->curr + ofs;
 }
 
+void *
+lwsac_use_zeroed(struct lwsac **head, size_t ensure, size_t chunk_size)
+{
+	void *r = lwsac_use(head, ensure, chunk_size);
+
+	if (r)
+		memset(r, 0, ensure);
+
+	return r;
+}
+
 void
 lwsac_free(struct lwsac **head)
 {